The usefulness of ethylene-propylene rubber ("EPR"), the general term for ethylene-alpha-olefin copolymer ("EPC")/ethylene-alpha-olefin-diene monomer ("EPDM") elastomeric polymers, for improving the impact strength of polypropylene ("PP") plastic compositions is known. The improvement may be generally accomplished through producing a simple physical mixture of PP with EPR.
For example, U.S. Pat. No. 4,087,485, to Huff, is directed to improving the impact strength of a polypropylene composition by incorporating therein minor amounts of polyethylene and ethylene-propylene copolymer.
It is recognized that two or more polymers may be blended together to form a wide variety of random or structured morphologies to obtain products that potentially offer desirable combinations of characteristics. However, it may be difficult or impossible in practice to achieve many potential combinations through simple blending because of some inherent and fundamental problems. Frequently, the two polymers are thermodynamically immiscible, which precludes generating a truly homogeneous product. This immiscibility may not be a problem per se since often it is desirable to have a two-phase structure. However, the situation at the interface between these two phases very often does lead to problems. The typical case is one of high interfacial tension and poor adhesion between the two phases. This interfacial tension contributes, along with high viscosities, to the inherent difficulty of imparting the desired degree of dispersion to random mixtures and to their subsequent lack of stability, giving rise to gross separation or stratification during later processing or use. Poor adhesion leads, in part, to the very weak and brittle mechanical behavior often observed in dispersed blends and may render some highly structured morphologies impossible.
It is extremely desirable to prepare a graft copolymer having the impact strength of polypropylene and the elastomeric properties of EPR and to extend the resultant copolymer with a high oil or low molecular weight component content to obtain a soft material having a low Shore A hardness.
Thus, the oil or low molecular weight component extended graft polymers of this invention, comprising a maleated EPR grafted to a maleated polypropylene by the use of a difunctional grafting agent reactive with the maleate groups on the EPR and the polypropylene, are believed to be unknown prior to the disclosure herein.